Dual capillary spinneret for production of homofilament crimp fibers

ABSTRACT

Robust homofilament fibers are meltspun from a differently shaped dual capillary spinneret design to induce differential fiber morphology to produce crimping. Crimping may further be aided by quenching and drawing of the fibers.

FIELD OF THE INVENTION

[0001] The present invention relates generally to lofty nonwoven fiberwebs. The present invention relates specifically to lofty nonwoven fiberwebs of homofilament crimped fibers and dual capillary means and methodfor producing the web.

BACKGROUND OF THE INVENTION

[0002] Webs of homofilament crimped thermoplastic fibers are useful forvarious fluid handling or retaining materials and the like because oftheir open structure, resiliency, and economy of manufacture.Particularly, the use of a single thermoplastic polymer in the making ofthe crimped fibers is good for economical and consistent manufacture.However, the present state of the manufacturing art relies largely onbicomponent filaments to induce the desired level of crimping in aconsistent fashion leading to certain compromises in the consistency offabric characteristics and economy thereof.

[0003] In the known art several attempts have been made to producecrimping through shaped fibers. Spinnerets having shaped orifices ormultiple orifices to produce the shaped fibers are also known. Howeverthe known art suffers in several regards. First, the known processing ofthe shaped fibers is not a robust process in that the fibers are notconsistently shaped or the component parts of the fiber do not holdtogether well, resulting in less predictable web morphology andattendant functional characteristics. Second, the degree of crimpingderived from using a single polymer to produce a crimped homofilamenthas not always attained the desired level.

[0004] Therefore, there is a need in the art for a robust and easilyaccomplished means and method of manufacturing homofilament crimpedfiber which has a high degree of crimp and good predictability of thefiber shape and crimping to yield the desired nonwoven web structure.

Definitions

[0005] Within the context of this specification, each term or phrasebelow will include the following meaning or meanings.

[0006] “Article” refers to a garment or other end-use article ofmanufacture, including but not limited to, diapers, training pants, swimwear, catamenial products, medical garments or wraps, and the like.

[0007] “Bonded” or “bonding” refers to the joining, adhering,connecting, attaching, or the like, of two elements. Two elements willbe considered to be bonded together when they are bonded directly to oneanother or indirectly to one another, such as when each is directlybonded to intermediate elements.

[0008] “Connected” refers to the joining, adhering, bonding, attaching,or the like, of two elements. Two elements will be considered to beconnected together when they are connected directly to one another orindirectly to one another, such as when each is directly connected tointermediate elements.

[0009] “Disposable” refers to articles which are designed to bediscarded after a limited use rather than being laundered or otherwiserestored for reuse.

[0010] “Disposed,” “disposed on,” and variations thereof are intended tomean that one element can be integral with another element, or that oneelement can be a separate structure bonded to or placed with or placednear another element.

[0011] “Fabrics” is used to refer to all of the woven, knitted andnonwoven fibrous webs.

[0012] “Homofilament” refers to a fiber formed from only one predominatepolymer and made from a single stream of that polymer. This is not meantto exclude fibers formed from one polymer to which small amounts ofadditives have been added for coloration, anti-static properties,lubrication, hydrophilicity, etc.

[0013] “Integral” or “Integrally” is used to refer to various portionsof a single unitary element rather than separate structures bonded to orplaced with or placed near one another.

[0014] “Layer” when used in the singular can have the dual meaning of asingle element or a plurality of elements.

[0015] “Meltblown fiber” means fibers formed by extruding a moltenthermoplastic material through a plurality of fine, usually circular,die capillaries as molten threads or filaments into converging highvelocity heated gas (e.g., air) streams which attenuate the filaments ofmolten thermoplastic material to reduce their diameter, which may be tomicrofiber diameter. Thereafter, the meltblown fibers are carried by thehigh velocity gas stream and are deposited on a collecting surface toform a web of randomly dispersed meltblown fibers. Such a process isdisclosed for example, in U.S. Pat. No. 3,849,241 to Butin et al.Meltblown fibers are microfibers which may be continuous ordiscontinuous, are generally smaller than about 0.6 denier, and aregenerally self bonding when deposited onto a collecting surface.Meltblown fibers used in the present invention are preferablysubstantially continuous in length.

[0016] “Meltspun” refers generically to a fiber which is formed from amolten polymer by a fiber-forming extrusion process, for example, suchas are made by the meltblown and spunbond processes.

[0017] “Member” when used in the singular can have the dual meaning of asingle element or a plurality of elements.

[0018] “Nonwoven” and “nonwoven web” refer to materials and webs ofmaterial which are formed without the aid of a textile weaving orknitting process.

[0019] “Polymers” include, but are not limited to, homopolymers,copolymers, such as for example, block, graft, random and alternatingcopolymers, terpolymers, etc. and blends and modifications thereof.Furthermore, unless otherwise specifically limited, the term “polymer”shall include all possible geometrical configurations of the material.These configurations include, but are not limited to isotactic,syndiotactic and atactic symmetries.

[0020] Words of degree, such as “About”, “Substantially”, and the likeare used herein in the sense of “at, or nearly at, when given themanufacturing and material tolerances inherent in the statedcircumstances” and are used to prevent the unscrupulous infringer fromunfairly taking advantage of the invention disclosure where exact orabsolute figures are stated as an aid to understanding the invention.

[0021] “Spunbond fiber” refers to small diameter fibers which are formedby extruding molten thermoplastic material as filaments from a pluralityof fine capillaries of a spinneret having a circular or otherconfiguration, with the diameter of the extruded filaments then beingrapidly reduced as by, for example, in U.S. Pat. No. 4,340,563 to Appelet al., and U.S. Pat. No. 3,692,618 to Dorschner et al., U.S. Pat. No.3,802,817 to Matsuki et al., U.S. Pat. Nos. 3,338,992 and 3,341,394 toKinney, U.S. Pat. No. 3,502,763 to Hartmann, U.S. Pat. No. 3,502,538 toPetersen, and U.S. Pat. No. 3,542,615 to Dobo et al., each of which isincorporated herein in its entirety by reference. Spunbond fibers arequenched and generally not tacky when they are deposited onto acollecting surface. Spunbond fibers are generally continuous and oftenhave average deniers larger than about 0.3, more particularly, betweenabout 0.6 and 10.

[0022] “Surface” includes any layer, film, woven, nonwoven, laminate,composite, or the like, whether pervious or impervious to air, gas,and/or liquids.

[0023] “Thermoplastic” describes a material that softens when exposed toheat and which substantially returns to a nonsoftened condition whencooled to room temperature.

[0024] These terms may be defined with additional language in theremaining portions of the specification.

SUMMARY OF THE INVENTION

[0025] A homofilament crimped fiber is produced by joining polymerstreams exiting through a dual capillary spinneret design. Differentlyinduced shear in the different polymer streams results in differentialtensions in the joined halves of the filament. The filaments may furtherbe subjected to differential or directed quenching which provides forsetting the crimps in the filaments to further induce the crimp. Thefilaments may also be desirably drawn out in the spinning processing toachieve a substantially round shape which results in a robust andpredictable filament.

[0026] The dual capillary design for producing a crimped homofilamentfiber according to the present invention has a first capillary and asecond capillary spaced apart at a distance sufficiently close to have asingle filament formed from concurrent liquid polymer extrusions fromthe first capillary and the second capillary. The capillaries share aparallel border where they are adjacent each other and are specificallyshaped to maximize induced shear. Specific shapes of spinneret orificesand methodologies for using those shapes will be further elaborated onbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1 shows a known apparatus of the general environment used formanufacturing filaments according to the present invention.

[0028]FIG. 2 is a schematic representation of a cross sectional view ofthe exemplary fiber forming dual capillaries of the present inventionand surrounding elements of a meltspun die.

[0029]FIG. 3 is a first exemplary dual capillary design for producingcrimped homofilament fibers according to the present invention.

[0030]FIG. 4 is a second exemplary dual capillary design for producingcrimped homofilament fibers according to the present invention.

[0031]FIG. 5 is a third exemplary dual capillary design for producingcrimped homofilament fibers according to the present invention.

[0032]FIG. 6 is a fourth exemplary dual capillary design for producingcrimped homofilament fibers according to the present invention.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

[0033] The present invention provides a method of producing homofilamenthelical crimped nonwoven web. The present invention is usable withmeltspun polymers known to those skilled in the art and mostsurprisingly works well with polypropylene polymers. In general, themeans and method of the present invention comprise using dual shapedcapillaries for inducing differential shear between polymer flowing in afirst shaped capillary and the polymer flowing in a second differentlyshaped capillary. The method may further include differential ordirected quenching of the filaments. The method may also include drawingthe fibers to a round cross sectional shape while still in their plasticstate.

[0034] In a preferred embodiment of the present invention, the fibersmay be formed of resin which is preferably a thermoplastic polypropylenepolymer. Other polymers such as, but not limited to, polyolefins,polyesters, polyamides, polyurethanes, copolymers and mixtures thereofmight also be used in accordance with certain aspects of the presentinvention.

[0035]FIG. 1 shows an apparatus of the general environment used formanufacturing filaments, or “fibers” as used synonymously therewith,according to the present invention. Apparatus 10 has a first assembly 12for producing spunbond fibers in accordance with known methods. Aspinneret 14 is supplied with molten polymer resin from a resin source(not shown). The spinneret 14 produces fine denier fibers from the exit16, which are quenched by an air stream supplied by a quench blower 18.The air stream differentially cools one side of the fiber stream morethan the other side, thus causing bending and crimping of the fibers.Crimping, as discussed in general hereinabove, creates a softer fabricby reducing the “straightness” of the fibers, between bond pointscreated in the thermal bonding step, as well as fiber-to-fiber bonds.Various parameters of the quench blower 18 can be controlled to controlthe quality and quantity of crimping. Fiber composition and resinselection also determine the crimping characteristics imparted.

[0036] The filaments are drawn into a fiber drawing unit or aspirator 20having a Venturi tube/channel 22, through which the fibers pass. Thetube is supplied with temperature controlled air, which attenuates thefilaments as they are pulled through the fiber drawing unit 20. Theattenuated fibers are then deposited onto a foraminous moving collectionbelt 24 and retained on the belt 24 by a vacuum force exerted by avacuum box 26. The belt 24 travels around guide rollers 27. As thefibers move along on the belt 24, a compaction roll 28 above the belt,which operates with one of the guide rollers 27 beneath the belt,compresses the spunbond mat so that the fibers have sufficient integrityto go through the manufacturing process.

[0037] As shown in FIG. 2, die tip 70 defines a polymer supply passage72 that terminates in further passages defined by counterbores 74 whichare connected to capillaries 76. While schematic in nature, it will beappreciated that FIG. 2 shows dual capillaries 76 which are individualpassages formed in the die tip 70. The differential capillary shapes aremore clearly seen in FIG. 3. Generally, it is preferred that thecapillaries of the present invention have a length to width ratio ofbetween about 4:1 to about 12:1; and more preferably between about 6:1to about 10:1, with length being defined in the direction of polymerflow and width being the capillary diameter.

[0038] According to the present invention, each fiber is produced by thetwo capillaries of a dual capillary design. FIGS. 3-6 detail exemplaryembodiments of these dual capillary designs according to the presentinvention. It is believed that use of differently shaped capillaries toproduce a single fiber causes the one side of the fiber with increasedshear to have a lower viscosity and lower melt strength withsubsequently higher orientation within that segment of the fiber.Differential polymer structure between the two capillaries is furtherbelieved to result in differential cooling rates between fiber segments,further helping to produce crimp.

[0039] As seen in FIG. 3, the dual capillary design 112 has a firstcapillary 114 and a second capillary 116. The first capillary 114 has anoutside border 118 and an inside border 120 located adjacent the secondcapillary 116 at a distance sufficiently close to cause polymerextrudate from the first and second capillaries to meld or conjoin intoa single fiber. The outside border 118 is arcuate and extends over about120°. The inside border 120 is also arcuate and extends over about 120°but has a smaller radius than the outside border. The second capillary116 is shown as substantially circular such that its inside border 122,facing and adjacent the first capillary 114, is arcuate. The secondcapillary distal border 124, that is distal from the first capillary, isof course also arcuate. The second capillary while shown as circular maybe substantially elliptical if desired.

[0040] Referencing FIG. 4, a dual capillary design 126 similar to FIG. 3has a circular second capillary 128 like the design of FIG. 3. The firstcapillary 130, like FIG. 3, also has arcuate inside and outside borders132 and 134, respectively, but the arcs extend over about 180°.

[0041] Referencing FIG. 5, the dual capillary design 136 has asubstantially half round first capillary 138 with an arcuate outsideborder 140 and a flat inside border 142 adjacent the second capillary144. The second capillary has a flat inside border 146 adjacent thefirst capillary inside border 142 and of substantially the same length.The overall shape of the second capillary 144 is that of a squared-offarch, with the distal border 148 of the second capillary 144 containinga squared-off “U” shape 150 with the bight of the “U” extending towardsthe second capillary inside border 146.

[0042] Referencing FIG. 6, a dual capillary design 152 similar to FIG. 5has a first capillary 154 with a smaller chorded section of a circulararea than the half round first capillary of FIG. 5. The first capillaryoutside border 156 is again arcuate while the inside border 158 is flat.The overall shape of the second capillary 160 is again substantiallyarch-shaped with its inside border 162 being flat and slightly longerthan or coextensive with the inside border 158 of the first capillary154. The distal border 164 of the second capillary forms a “V”-shapedarch 166 of about 90° with the point of the arch extending towards thesecond capillary inside border 162.

[0043] Further, during processing of the extrudate, quick application ofthe quenching fluid to both sides of the fiber is believed to best helpfix the stress differentials induced by the dual capillaries and aid inoverall crimping. Quenching fluid may alternatively be directed towardsa particular orientation of the dual capillary design in order to affectcrimping. It was generally found that quenching directed toward the morehighly shaped capillary side resulted in smaller crimps.

[0044] Having thus described means and method for producing homofilamentcrimped thermoplastic fibers through the use of dual capillaries, itwill be appreciated that while this invention has been described inrelation to certain preferred embodiments thereof, and many details havebeen set forth for purpose of illustration, it will be apparent to thoseskilled in the art that the invention is susceptible to additionalembodiments and that certain of the details described herein can bevaried considerably without departing from the basic principles of theinvention.

We claim:
 1. A dual capillary design for producing a crimpedhomofilament fiber consisting of: a first capillary having an a firstcapillary inside border and a first capillary outside border, the firstcapillary outside border being curved; a second capillary spaced fromthe first capillary at a distance sufficiently close to have a singlefilament formed from concurrent liquid polymer extrusions from the firstcapillary and the second capillary; the second capillary having a secondcapillary inside border proximal to the first capillary inside borderand a second capillary outside border distal from the first capillaryinside border, the first capillary inside border and the secondcapillary inside border being parallel; whereby concurrent liquidpolymer extrusions from the first capillary and the second capillaryconjoin to form a single filament having sections of different inducedshear thereby causing the filament to crimp.
 2. The dual capillarydesign of claim 1, wherein the first capillary is arcuate with bothinside and outside borders being substantially curved.
 3. The dualcapillary design of claim 2, wherein the second capillary issubstantially circular or substantially elliptical.
 4. The dualcapillary design of claim 1, wherein the second capillary issubstantially arch-shaped.
 5. The dual capillary design of claim 4,wherein the second capillary inside border is flat.
 6. The dualcapillary design of claim 4, wherein the first capillary is arcuate onits outside border and flat on its inside border.
 7. A process formaking crimped fibers, comprising the step of: extruding a liquidpolymer from a first capillary having an a first capillary inside borderand a first capillary outside border, the first capillary outside borderbeing curved; extruding the liquid polymer from a second capillaryhaving an second capillary inside border proximal to the first capillaryinside border and a second capillary outside border distal from thefirst capillary inside border, the first capillary inside border and thesecond capillary inside border being parallel; and forming a singlefilament from concurrent liquid polymer extrusions from the first andsecond capillaries, the filament having conjoined sections from each ofthe first capillary and the second capillary; each conjoined sectionhaving a different induced shear thereby causing the filament to crimp.8. The process for making crimped fibers of claim 7, wherein the fibersare polypropylene.
 9. The process for making crimped fibers according toclaim 7, further comprising the step of directing quenching fluid atboth sides of the fiber.
 10. The process for making crimped fibersaccording to claim 7, further comprising the step of: drawing the fiberswhile in their plastic state to produce fibers with a substantiallyround cross section.
 11. The process for making crimped fibers accordingto claim 9, further comprising the step of: drawing the fibers while intheir plastic state to produce fibers with a substantially round crosssection.
 12. A nonwoven web comprising a plurality of fibers made fromthe apparatus according to claim
 1. 13. A nonwoven web comprising aplurality of fibers made according to the method of claim
 7. 14. Thenonwoven web of claim 12, wherein the fibers are polypropylene.
 15. Thenonwoven web of claim 13, wherein the fibers are polypropylene.
 16. Aspinneret design for producing a crimped homofilament fiber comprising:a) an extruder for forcing a liquid polymer through spinneretcapillaries; b) a fiber forming portion consisting of: a first capillaryhaving an a first capillary inside border and a first capillary outsideborder, the first capillary outside border being curved; a secondcapillary spaced from the first capillary at a distance sufficientlyclose to have a single filament formed from concurrent liquid polymerextrusions from the first capillary and the second capillary; the secondcapillary having a second capillary inside border proximal to the firstcapillary inside border and a second capillary outside border distalfrom the first capillary inside border, the first capillary insideborder and the second capillary inside border being parallel; andwhereby concurrent liquid polymer extrusions from the first capillaryand the second capillary conjoin to form a single filament havingsections of different induced shear thereby causing the filament tocrimp.
 17. The spinneret design of claim 16, wherein at least one of thecapillaries has a length to width ratio of between about 4:1 to about12:1.
 18. The spinneret design of claim 16, wherein the capillaries areconnected to a polymer supply passage by a counterbore.